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Intraocular pressure after penetrating keratoplasty and Descemet's stripping automated endothelial keratoplasty
ORIGINAL ARTICLE
Intraocular pressure after penetrating keratoplasty and Descemet’s stripping automated endothelial keratoplasty Elad Moisseiev, MD, David Varssano, MD, Elkanah Rosenfeld, MD, Rony Rachmiel, MD ´ SUME ´ ABSTRACT ● RE Objective: To compare the intraocular pressure (IOP) during the first postoperative year after penetrating keratoplasty (PK) and Descemet’s stripping automated endothelial keratoplasty (DSAEK). Design: Retrospective chart review. Participants: Fifty-three pseudophakic eyes of 53 patients who underwent PK or DSAEK because of endothelial dysfunction between January 2006 and December 2010 were included. Methods: Surgeries consisted of 19 (35.8%) PK procedures and 34 (64.2%) DSAEK procedures. Demographic, preoperative, and postoperative data including IOP, number of medications, rejection and occurrence, and complications were recorded. Results: Patients who had undergone DSAEK had statistically significant lower IOP throughout 12 months after surgery than those who had undergone PK (p ¼ 0.028), despite similar use of IOP-lowering medications during this time. Measurements of postoperative IOP greater than 21 mm Hg and greater than 30 mm Hg were significantly more common in patients who had undergone PK than DSAEK (p ¼ 0.015 and 0.022, respectively). Complication rates were similar between the 2 groups. IOP was not correlated with patient age, sex, background illnesses, or previous glaucoma. Conclusions: IOP is significantly lower after DSAEK compared with PK. Several mechanisms explaining this difference are proposed. New corneal transplantation modalities such as DSAEK, with a better postoperative IOP control, may reduce the risk for later visual loss caused by postoperative glaucomatous damage. anne´e suivant une ke´ratoplastie perforante (KP) et une Objet : Comparaison de la pression intraoculaire (PIO) pendant la premiere ke´ratoplastie endothe´liale automatise´e par de´corticage de la Descemet (KEAD). Nature : Examen re´troactif des dossiers. Participants : Cinquante-trois yeux pseudophaques de 53 patients ayant subi une KP ou une KEAD pour disfonctionnement endothe´lial, entre janvier 2006 et de´cembre 2010. Me´thodes : Les chirurgies ont compris 19 (35,8 %) proce´dures KP et 34 (64,2 %) proce´dures KEAD. L’on a pris en compte des donne´es de´mographiques, pre´ et post ope´ratoires, y compris la pression intraoculaire (PIO), le nombre de me´dicaments, de re´jection et d’e´ve´nements et de complications. Re´sultats : Les patients qui avaient subi une KEAD avaient une PIO statistiquement moins e´leve´e dans les 12 mois suivant la ˆ chirurgie que ceux qui avaient subi une KP (p ¼ 0,028), malgre´ la meme utilisation de me´dicaments pour re´duire la PIO pendant ce temps. Les mesures postope´ratoires de la PIO plus hautes que 21 mmHg et plus hautes que 30 mmHg e´taient significativement plus communes chez les patients qui avaient rec- u une KP que chez ceux qui avaient rec- u une KEAD (p ¼ 0,015 et 0,022 respectivement). Les taux de complication e´taient semblables dans les deux groupes. La PIO n’e´tait pas ˆ associe´e a l’age, au genre, aux maladies ante´rieures ni au glaucome pre´ce´dant. la KEAD, comparativement a la KP. Plusieurs me´canismes Conclusion : La PIO est significativement moins e´leve´e apres expliquant cette diffe´rence ont e´te´ propose´s. Les nouvelles modalite´s de la transplantation de la corne´e, telle la KEAD, avec un ˆ meilleur controle postope´ratoire de la PIO, peuvent re´duire le risque d’une e´ventuelle perte visuelle due au dommage glaucomateux postope´ratoire.
Elevated intraocular pressure (IOP) and glaucoma are frequent complications of penetrating keratoplasty (PK), which may lead to irreversible vision loss.1–4 The incidence rate of glaucoma after PK ranges from 10% to 53% but is typically within the range of 15% to 30%.1–3,5–11 The cause of elevated IOP after PK is multifactorial and includes many causes such as angle distortion, collapse of the trabecular meshwork, tight corneal sutures, postoperative inflammation, formation of peripheral anterior synechiae (PAS), and response to prolonged steroidal treatment.1,2,8,12,13
Descemet’s stripping automated endothelial keratoplasty (DSAEK) has several significant advantages over PK. It allows more rapid healing and early visual recovery, requires no or only a few corneal sutures and does not induce astigmatism, and maintains the structural integrity of the recipient eye.11,14–16 This technique has gained increasing popularity in recent years, and it is currently considered the procedure of choice for endothelial dysfunction.11,16–18 Most studies reported rates of elevated IOP and glaucoma after DSAEK between 0% and 18%, but it has also been reported to be as high as 35%.11,19–21
From the Department of Ophthalmology, Tel Aviv Sourasky Medical Center; and Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel.
Can J Ophthalmol 2013;48:179–185 0008-4182/13/$-see front matter & 2013 Canadian Ophthalmological Society. Published by Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.jcjo.2013.01.003
Originally received Aug. 29, 2012. Final revision Dec. 29, 2012. Accepted Jan. 3, 2013 Correspondence to Elad Moisseiev, Department of Ophthalmology, Tel Aviv Medical Center, Weitzman 6 St., Tel Aviv, 64239 Israel; [email protected] CAN J OPHTHALMOL — VOL. 48, NO. 3, JUNE 2013
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Comparison of IOP after PK and DSAEK—Moisseiev et al. Mechanisms that may cause elevated IOP after DSAEK include pupillary block glaucoma, trapping of an air bubble behind the iris and subsequent angle closure, formation of PAS, and response to steroids.11,22 Several comparative studies have established the superiority of DSAEK over PK regarding visual rehabilitation.16,23,24 However, very sparse information exists in published literature regarding the comparative rates of IOP elevation between the 2 surgical techniques. During 12 months of postoperative follow-up, 1 study reported rates of induced glaucoma to be 6.3% after PK and 6.7% after DSAEK,16 and another reported rates of IOP over 25 mm Hg to be 16% after PK and 28% after DSAEK.25 Review of literature revealed no study that was directly focused at the comparison of IOP elevation between the 2 techniques. The purpose of this study was to investigate and describe the changes in IOP during the first postoperative year after PK and DSAEK, and reveal any differences between the 2 surgical techniques.
METHODS Patient selection
After approval by the Institutional Review Board of the Tel Aviv Medical Center, the records of all consecutive patients who underwent PK or DSAEK in our institution between January 1, 2006, and December 31, 2010, were retrospectively reviewed. All included patients were 18 years or older at the time of surgery, and their indication for surgery was either pseudophakic bullous keratopathy (PBK) or Fuchs endothelial dystrophy. Only pseudophakic patients with intraocular lens (IOL) within the capsular bag throughout the follow-up period were included. Inclusion in the study also required complete documentation of IOP by Goldmann applanation tonometry (GAT) at all of the following time points: before surgery, upon discharge, and 1 week, 1 month, 3 months, 6 months, and 12 months postoperatively. Patients whose indication for transplantation was due to trauma, herpetic keratitis or keratouveitis, any infectious cause, keratoconus, or a previous failed corneal graft were excluded. Only first procedures were included in this study. Patients who had undergone other techniques of corneal transplantation, or whose surgery was combined with any procedure other than cataract extraction and IOL implantation within the capsular bag were excluded. Phakic, aphakic, and pseudophakic patients with anterior chamber, iris fixated, or sulcus IOLs were excluded, as were patients who had previously undergone any other ocular surgery except cataract extraction. Exclusion criteria also included any history of retinal detachment, retinal vascular occlusion, advanced glaucomatous damage, optic neuropathy, or trauma. Patients who were previously treated with subconjunctival, sub-Tenon, or intravitreal steroid injections for any reason, or patients receiving
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systemic steroidal treatments were excluded. Patients with neovascular glaucoma, synechiae, or any previous glaucoma surgery were also excluded; only patients with no previous glaucoma or previous open-angle glaucoma that was controlled by topical treatment were included. In addition, patients whose records were incomplete were excluded from this study. Data collection
Data were retrieved from the medical notes before the surgery, the surgical reports, the in-patient department charts, and the outpatient clinic charts. The parameters recorded included demographic information, history of diabetes mellitus or hypertension, previous ocular history, the indication for the corneal transplantation, number of transplantation, lens status, occurrence of rejection and any postoperative complications, and the need for any additional medical or surgical interventions throughout the follow-up period. Together with the IOP measurements, the number of pressure-lowering agents in use at all time points was also recorded. Combination preparations (such as Cosopt (timolol and dorzolamide) and Combigan (timolol and brimonidine)) were counted as 2 separate agents. For patients who underwent additional procedures for the treatment of glaucoma, IOP values were censored after these procedures. The number of IOP-lowering agents after the procedure was still recorded and analyzed. Surgical parameters included review of surgical technique as documented to ensure uniformity and any additional procedures combined with the corneal transplantation. Parameters recorded for the donor cornea included donor age, number of days between harvest and transplantation, and endothelial cell count by the Noncon Robo SP-6000 specular microscope (Konan Medical, Inc., Hyogo, Japan) when available. Donor corneas were preserved in EUSOLC dextran corneal storage media containing gentamycin sulfate (143 mg/ml; AL.CHI.MI.A. SRL., Padova, Italy) and kept at 41C between harvest and surgery. Surgical techniques
Surgical technique for PK included creating a partial depth circular incision in the cornea using a trephine, followed by full-thickness excision of the recipient cornea using curved corneal scissors. The donor corneal button was cut by a punch trephine and sutured in place, typically using either 16 interrupted or 8 interrupted and one 16-byte running 10–0 nylon sutures. Surgical technique for DSAEK included stripping of central Descemet’s membrane and endothelium. The donor cornea was cut horizontally with a turbine-driven Moria CB Microkeratome (Moria, Versailles, France) and a 300-mm head. The posterior lamella was then trephined to the size chosen by the surgeon (typically 8.0–9.0 mm in diameter) and inserted into the anterior chamber using one of several techniques, including Busin and Tan glides
Comparison of IOP after PK and DSAEK—Moisseiev et al. Table 1—Baseline information of patients who underwent penetrating keratoplasty versus Descemet’s stripping automated endothelial keratoplasty Parameter
PK (n ¼ 19)
DSAEK (n ¼ 34)
75.8 10 (52.6) 5 (26.3) 14 (73.6) 15.52 6 (31.5) 0.15
74.5 15 (44.2) 7 (20.6) 21 (61.8) 15.53 14 (41.1) 0.25
Mean age, y Male sex, n (%) Diabetes mellitus, n (%) Hypertension, n (%) Mean preoperative IOP, mm Hg Previous glaucoma, n (%) Mean preoperative number of IOP-lowering agents
There was no statistically significant difference between groups in any of the parameters (p 4 0.05). PK, penetrating keratoplasty; DSAEK, Descemet’s stripping automated endothelial keratoplasty; IOP, intraocular pressure.
and suture pull-through. All wounds were sutured using interrupted 10–0 nylon sutures. Air was injected into the anterior chamber under the donor tissue. Either iridotomy or mydriatics were used to prevent pupillary block. Patients were instructed to remain supine for 3 to 6 hours after surgery. After both types of surgery, all patients were treated with topical ofloxacin 0.3% and either dexamethasone sulfate 0.1% or prednisolone acetate 1% four times a day. Dosage was tapered over a year after surgery. Statistical analysis
Correlations between continuous variables were analyzed using Pearson correlation coefficient. t test was used to compare continuous variables between groups. w2 test was used to analyze associations between categorical parameters. Analysis of variance with repeated measures over time was used to analyze the difference in IOP between the 2 surgical techniques. A p value of 0.05 was used to declare statistically significant difference between groups for all analyses. Data were analyzed using SPSS for Windows, version 17.
RESULTS Fifty-three eyes of 53 patients fulfilled the inclusion criteria and were included in the study. Surgeries consisted of 19 (35.8%) PK procedures and 34 (64.2%) DSAEK procedures. The patients in the study included 25 (47.1%) men and 28 (52.9%) women, with a mean age of 75.0 ⫾ 8.8 years (range 52–92 years). There was no statistically significant difference in any of the demographic parameters between both patient groups (Table 1).
Indications for surgery included 42 (79.2%) cases of PBK and 11 (20.8%) cases of Fuchs endothelial dystrophy. The distribution of the indications for surgery varied between the groups, as 9 (81.8%) of 11 cases who had surgery because of Fuchs endothelial dystrophy underwent DSAEK (Table 2). Mean corneal donor age was 59.8 ⫾ 15.0 years (range 12–80 years). Mean time between harvest and transplantation was 4.0 ⫾ 1.9 days (range 1–7 days). Endothelial cell count was available for 23 (43.4%) of the donor corneas and had a mean of 2736 ⫾ 274 cells/mm2 (range 2056–3205 cells/mm2). Donor age was significantly younger, and endothelial cell counts were significantly higher in DSAEK surgeries compared with PK. Time between harvest and surgery was similar in both groups (Table 3). IOP analysis
There was no significant difference in preoperative IOP values (Table 1) or the number of IOP-lowering agents used by patients who underwent PK or DSAEK. Analysis of variance with repeated measures over time was used to compare the IOP during the first 12 months after surgery between the 2 surgical techniques. Patients who had undergone DSAEK had statistically significant lower IOP throughout this period in comparison with those who had undergone PK (p ¼ 0.028; Fig. 1). The number of IOP-lowering agents was not statistically different at any time point between these 2 patient groups (Fig. 2, Table 4). Thirty-three (62.2%) patients were treated with at least 1 IOP-lowering agent at any point throughout the followup. At 12 months, 13 (68.4%) PK patients were treated with at least 1 IOP-lowering agent, compared with 18 (52.9%) DSAEK patients (p ¼ 0.27; Table 4). There was no significant difference in the number of hypotensive agents or the number of subjects who required IOPlowering medication between the groups. Surgical intervention to control elevated IOP was required in 5 (9.4%) patients (2 [11%] PK and 3 [9%] DSAEK; p ¼ 0.82) and was decided upon by glaucoma subspecialists who also monitored these patients. One patient (1.8%) who underwent PK required surgical synechiolysis because of formation of PAS, and another patient (1.8%) underwent Ahmed valve implantation. Two patients (3.7%) who had undergone DSAEK underwent trabeculectomy, and 1 patient (1.8%) underwent Ahmed valve implantation. IOP returned to the normal range in all 5 cases. Measurements of IOP values over 21 mm Hg or at any time point throughout the follow-up were recorded in 13
Table 2—Distribution of indications for surgery Indication for Surgery Pseudophakic bullous keratopathy, n (%) Fuchs endothelial dystrophy, n (%)
Total (N ¼ 53)
PK (n ¼ 19)
DSAEK (n ¼ 34)
p
42 (79.2) 11 (20.8)
17 (89.4) 2 (10.6)
25 (73.5) 9 (26.5)
0.14 0.18
PK, penetrating keratoplasty; DSAEK, Descemet’s stripping automated endothelial keratoplasty
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Comparison of IOP after PK and DSAEK—Moisseiev et al. Table 3—Donor cornea information and comparison between penetrating keratoplasty and Descemet’s stripping automated endothelial keratoplasty Donor Cornea Parameter Mean donor age, y Time between harvest and surgery, days Mean endothelial count, cells/mm2
Total
PK
DSAEK
p
59.8 4.0 2736 (N ¼ 23)
65.8 4.2 2587 (n ¼ 10)
56.5 3.9 2850 (n ¼ 13)
0.029 40.05 0.018
PK, penetrating keratoplasty; DSAEK, Descemet’s stripping automated endothelial keratoplasty
(68.4%) patients who had undergone PK and 9 (26.5%) patients who had undergone DSAEK. This difference was statistically significant (p ¼ 0.015). Measurements of IOP values over 30 mm Hg at any time point throughout the follow-up were recorded in 6 (31.5%) patients who had undergone PK and 5 (14.7%) patients who had undergone DSAEK. This difference was also statistically significant (p ¼ 0.022; Fig. 3). Neither indication for surgery was correlated with IOP. Patient age, sex, and the presence of diabetes mellitus or hypertension did not correlate with IOP. Glaucoma before surgery did not correlate with IOP and was not associated with an increased rate of IOP measurements greater than 21 or 30 mm Hg throughout the follow-up period. These findings were also maintained in a separate analysis for each surgical technique. Combination of corneal transplantation with cataract extraction also did not correlate with IOP.
Complications
Rejection occurred within 12 months of surgery in 1 (1.9%) case in our series. The patient underwent PK and was treated for rejection with intensive topical steroidal treatment 3 months after the procedure.
Fig. 1 — Comparison of mean intraocular pressure values between patients who underwent penetrating keratoplasty (PKP) and Descemet’s stripping automated endothelial keratoplasty (DSAEK) at the measured time points throughout 12 months after surgery. The differences were statistically significant at all postoperative time points.
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Complications encountered during the follow-up period included 2 (3.8%) persistent large corneal erosions and 2 (3.8%) corneal ulcers. Both cases with persistent corneal erosions occurred in patients who underwent PK. One patient in each group was complicated by a corneal ulcer. Although the occurrence of rejection and other postoperative complications was higher in patients who had undergone PK, they did not correlate with IOP.
DISCUSSION This is the first study, to our knowledge, to directly compare IOP elevation between 2 common techniques of corneal transplantation, DSAEK and PK. We found that DSAEK is associated with significantly lower postoperative IOP than PK (Fig. 1), despite similar use of IOPlowering agents during the study period (Fig. 2). This finding has been significantly demonstrated in our study over 12 months of follow-up after surgery in pseudophakic patients who underwent corneal transplantation because of endothelial dysfunction. Complication rates were similar in both groups of patients. Endothelial dysfunction caused by Fuchs endothelial dystrophy or PBK currently constitutes the most common indication for corneal transplantation.11 Both indications are suitable for treatment by PK or DSAEK, but DSAEK is usually favored in Fuchs endothelial dystrophy.16,24,25
Fig. 2 — Comparison of mean number of intraocular pressure–lowering agents used by patients who underwent penetrating keratoplasty (PKP) and Descemet’s stripping automated endothelial keratoplasty (DSAEK), at the measured time points throughout 12 months after surgery. No statistically significant differences were found between the 2 groups.
Comparison of IOP after PK and DSAEK—Moisseiev et al. Table 4—Number and percentage of penetrating keratoplasty and Descemet’s stripping automated endothelial keratoplasty patients who were treated with at least intraocular pressure–lowering agent at all time points Group PK (N ¼ 19) DSAEK (N ¼ 34)
Before Surgery 6 (31.5%) 14 (41.1%)
1 wk
1 mo
3 mo
6 mo
12 mo
9 (47.3%) 11 (32.3%)
10 (52.6%) 15 (44.1%)
13 (68.4%) 17 (50%)
11 (57.9%) 18 (52.9%)
13 (68.4%) 18 (52.9%)
There was no significant difference between the groups at any time point. PK, penetrating keratoplasty; DSAEK, Descemet’s stripping automated endothelial keratoplasty.
Our results reflect this clinical preference, as most patients with Fuchs endothelial dystrophy underwent DSAEK (Table 2). However, only these 2 indications were included in this study, and they were grouped together because they share a common underlying pathologic mechanism of endothelial dysfunction, are treatable by both PK and DSAEK, and have similar outcomes by both surgical procedures.16,23–25 The purpose of this study was to compare IOP between PK and DSAEK. Patients were grouped accordingly. To reduce confounding factors that may interfere with proper comparison, we used strict inclusion and exclusion criteria, and the 2 groups are basically homogenous regarding patient age, sex, indication for surgery, lens status and ocular anatomy, previous background, ocular history, and baseline IOP (Table 2). The only significant differences between the 2 groups concern the donor cornea, which came from younger donors and had higher endothelial counts in patients who underwent DSAEK (Table 3). These differences represent a selection bias of donor corneas for DSAEK procedures but may be compensated by the higher early postoperative rate of endothelial cell loss compared with PK.25–28 Measurements of IOP greater than 21 mm Hg and greater than 30 mm Hg throughout this time were significantly more common in patients who underwent PK (Fig. 3). This finding is in accordance with a previous study that reported a higher incidence of IOP greater than
Fig. 3 — The occurrence of intraocular pressure elevation greater than 21 mm Hg and greater than 30 mm Hg throughout the follow-up period in patients who underwent penetrating keratoplasty (PKP) and Descemet’s stripping automated endothelial keratoplasty (DSAEK). The differences were statistically significant.
25 mm Hg after PK compared with DSAEK.25 Need of medical and surgical interventions to control IOP was not significantly different between the groups. No study had previously focused on this issue, and published literature offers no explanation to this difference. We propose several possible reasons for the tendency of IOP to be higher after PK. First, PK mandates disruption of the structural integrity of the eye, and it is likely that angle distortion and collapse of the trabecular meshwork are more significant during this procedure than in DSAEK. Second, it is possible that postoperative intraocular inflammation and formation of PAS are more frequent and severe after PK. This may also be related to the disruption of ocular integrity during surgery. Third, numerous tight corneal sutures are required in PK, and they may cause additional angle distortion in comparison with DSAEK, which is virtually sutureless. Finally, it is possible to speculate that the difference in IOP is related to differences in steroidal or IOP-lowering treatments. However, no significant differences between the 2 groups in respect to these 2 factors were noted in this study, and we believe that they did not attribute to the difference demonstrated in our study. The accuracy of GAT is known to be influenced by central corneal thickness (CCT),29,30 and it is possible to assume that the difference in IOP is due to changes in CCT. However, several studies have demonstrated that measurement of IOP by GAT was not influenced by CCT in post-PK eyes2,8,31–33 or in post-DSAEK eyes.33–36 It has also been demonstrated that DSAEK grafts are thicker than PK grafts for up to 12 months after surgery.24,37 Therefore, although CCT was not measured in our study, we conclude it is not the cause of the difference in IOP between the 2 groups. We acknowledge that post-PK and post-DSAEK grafts have different biomechanical properties that may influence IOP measurement by GAT, but measuring these characteristics in vivo is difficult in a clinical setting and is beyond the scope of our study. Previous glaucoma has been correlated with an increased risk for postoperative glaucoma both after PK and DSAEK.1,3,5,21,38,39 Our results did not demonstrate this correlation, and we believe this is due to the exclusion of most types of preexisting glaucoma and the inclusion of only a small number of patients with nonadvanced openangle glaucoma in our study. This is supported by the fact that in the subset of patients with prior glaucoma, the mean number of IOP-lowering agents used before the CAN J OPHTHALMOL — VOL. 48, NO. 3, JUNE 2013
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Comparison of IOP after PK and DSAEK—Moisseiev et al. corneal transplantation was only 1.2, and there was no significant difference in the number of IOP-lowering agents after the transplantation between them and patients without prior glaucoma. Rates of complications other than elevated IOP in this series are comparable with previously published data. Persistent epithelial defects were unique to PK, as expected.25 Graft survival rates have been shown to be equivalent in both PK and DSAEK.16,23–25 Our study included only 1 rejection of a PK graft. Despite this, we believe the series reflects the similar and excellent rates of success of both techniques in patients with endothelial dysfunction. This study is limited by its retrospective nature and medium sample size. However, we believe that the relatively high homogeneity between the groups and wholesomeness of the recorded data partly compensate for these limitations. Another limitation is that IOP-lowering medications were not administered according to a fixed standardized protocol. In general, maintenance of IOP less than 20 mm Hg was the goal of treatment in all patients. We are not aware of any difference in IOP tolerance between the 2 groups. CCT was not measured, and IOP was measured only by GAT and not by any other method that may be more accurate in postkeratoplasty eyes. We note that CCT was not found to influence IOP measurement by GAT in these eyes.2,8,31–36 Another limitation is that IOP measurement by GAT in eyes that underwent PK may be inaccurate regardless of CCT, because irregular astigmatism may result in uneven mires and complicate the GAT measurement and its interpretation. In conclusion, DSAEK is associated with a lower postoperative IOP than PK. This finding is demonstrated significantly by our study over 12 months after surgery in pseudophakic patients who underwent corneal transplantation because of endothelial dysfunction. DSAEK is already the preferred procedure by both corneal surgeons and patients for the treatment of this indication because of its superior visual rehabilitation and better tolerability.11,16–18,23,24 Our results indicate a new advantage of DSAEK over PK and serve to strengthen its preference by practicing ophthalmologists. The lower postoperative IOP after DSAEK may be beneficial in preventing late irreversible visual loss caused by glaucoma in these eyes, in which vision may already be compromised and IOP measurement may be difficult and inaccurate. Further research is required to corroborate our findings in prospective and large-scale studies.
Disclosure: The authors have no proprietary or commercial interest in any materials discussed in this article. REFERENCES 1. Foulks GN. Glaucoma associated with penetrating keratoplasty. Ophthalmology. 1987;94:871-4.
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38.
39.
tonometry in normal corneas and in eyes with automated lamellar and penetrating keratoplasty. Eye. 2011;25:642-50. Chang DTW, Pantcheva MB, Noecker RJ. Corneal thickness and intraocular pressure in edematous corneas before and after descemet stripping with automated endothelial keratoplasty. Cornea. 2010;29:1125-30. Mawatari Y, Kobayashi A, Yokogawa H, Sugiyama K. Intraocular pressure after descemet’s stripping and non-descemet’s stripping automated endothelial keratoplasty. Jpn J Ophthalmol. 2011; 55:98-102. Bochmann F, Kaufmann C, Becht C, Bachmann LM, Thiel MA. Comparison of dynamic contour tonometry with Goldmann applanation tonometry following descemet’s stripping automated endothelial keratoplasty (DSAEK). Klin Monbl Augenheilkd. 2009;226:241-4. Uchino Y, Shimmura S, Yamaguchi T, et al. Comparison of corneal thickness and haze in DSAEK and penetrating keratoplasty. Cornea. 2011;30:287-90. Allen MB, Lieu P, Mootha VV, et al. Risk factors for intraocular pressure elevation after descemet stripping automated endothelial keratoplasty. Eye Contact Lens. 2010;36:223-7. Quek DT, Wong T, Tan D, Mehta JS. Corneal graft survival and intraocular pressure control after descemet stripping automated endothelial keratoplasty in eyes with pre-existing glaucoma. Am J Ophthalmol. 2011;152:48-54.
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Intraocular pressure after penetrating keratoplasty and Descemet’s stripping automated endothelial keratoplasty Elad Moisseiev, MD, David Varssano, MD, Elkanah Rosenfeld, MD, Rony Rachmiel, MD ´ SUME ´ ABSTRACT ● RE Objective: To compare the intraocular pressure (IOP) during the first postoperative year after penetrating keratoplasty (PK) and Descemet’s stripping automated endothelial keratoplasty (DSAEK). Design: Retrospective chart review. Participants: Fifty-three pseudophakic eyes of 53 patients who underwent PK or DSAEK because of endothelial dysfunction between January 2006 and December 2010 were included. Methods: Surgeries consisted of 19 (35.8%) PK procedures and 34 (64.2%) DSAEK procedures. Demographic, preoperative, and postoperative data including IOP, number of medications, rejection and occurrence, and complications were recorded. Results: Patients who had undergone DSAEK had statistically significant lower IOP throughout 12 months after surgery than those who had undergone PK (p ¼ 0.028), despite similar use of IOP-lowering medications during this time. Measurements of postoperative IOP greater than 21 mm Hg and greater than 30 mm Hg were significantly more common in patients who had undergone PK than DSAEK (p ¼ 0.015 and 0.022, respectively). Complication rates were similar between the 2 groups. IOP was not correlated with patient age, sex, background illnesses, or previous glaucoma. Conclusions: IOP is significantly lower after DSAEK compared with PK. Several mechanisms explaining this difference are proposed. New corneal transplantation modalities such as DSAEK, with a better postoperative IOP control, may reduce the risk for later visual loss caused by postoperative glaucomatous damage. anne´e suivant une ke´ratoplastie perforante (KP) et une Objet : Comparaison de la pression intraoculaire (PIO) pendant la premiere ke´ratoplastie endothe´liale automatise´e par de´corticage de la Descemet (KEAD). Nature : Examen re´troactif des dossiers. Participants : Cinquante-trois yeux pseudophaques de 53 patients ayant subi une KP ou une KEAD pour disfonctionnement endothe´lial, entre janvier 2006 et de´cembre 2010. Me´thodes : Les chirurgies ont compris 19 (35,8 %) proce´dures KP et 34 (64,2 %) proce´dures KEAD. L’on a pris en compte des donne´es de´mographiques, pre´ et post ope´ratoires, y compris la pression intraoculaire (PIO), le nombre de me´dicaments, de re´jection et d’e´ve´nements et de complications. Re´sultats : Les patients qui avaient subi une KEAD avaient une PIO statistiquement moins e´leve´e dans les 12 mois suivant la ˆ chirurgie que ceux qui avaient subi une KP (p ¼ 0,028), malgre´ la meme utilisation de me´dicaments pour re´duire la PIO pendant ce temps. Les mesures postope´ratoires de la PIO plus hautes que 21 mmHg et plus hautes que 30 mmHg e´taient significativement plus communes chez les patients qui avaient rec- u une KP que chez ceux qui avaient rec- u une KEAD (p ¼ 0,015 et 0,022 respectivement). Les taux de complication e´taient semblables dans les deux groupes. La PIO n’e´tait pas ˆ associe´e a l’age, au genre, aux maladies ante´rieures ni au glaucome pre´ce´dant. la KEAD, comparativement a la KP. Plusieurs me´canismes Conclusion : La PIO est significativement moins e´leve´e apres expliquant cette diffe´rence ont e´te´ propose´s. Les nouvelles modalite´s de la transplantation de la corne´e, telle la KEAD, avec un ˆ meilleur controle postope´ratoire de la PIO, peuvent re´duire le risque d’une e´ventuelle perte visuelle due au dommage glaucomateux postope´ratoire.
Elevated intraocular pressure (IOP) and glaucoma are frequent complications of penetrating keratoplasty (PK), which may lead to irreversible vision loss.1–4 The incidence rate of glaucoma after PK ranges from 10% to 53% but is typically within the range of 15% to 30%.1–3,5–11 The cause of elevated IOP after PK is multifactorial and includes many causes such as angle distortion, collapse of the trabecular meshwork, tight corneal sutures, postoperative inflammation, formation of peripheral anterior synechiae (PAS), and response to prolonged steroidal treatment.1,2,8,12,13
Descemet’s stripping automated endothelial keratoplasty (DSAEK) has several significant advantages over PK. It allows more rapid healing and early visual recovery, requires no or only a few corneal sutures and does not induce astigmatism, and maintains the structural integrity of the recipient eye.11,14–16 This technique has gained increasing popularity in recent years, and it is currently considered the procedure of choice for endothelial dysfunction.11,16–18 Most studies reported rates of elevated IOP and glaucoma after DSAEK between 0% and 18%, but it has also been reported to be as high as 35%.11,19–21
From the Department of Ophthalmology, Tel Aviv Sourasky Medical Center; and Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel.
Can J Ophthalmol 2013;48:179–185 0008-4182/13/$-see front matter & 2013 Canadian Ophthalmological Society. Published by Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.jcjo.2013.01.003
Originally received Aug. 29, 2012. Final revision Dec. 29, 2012. Accepted Jan. 3, 2013 Correspondence to Elad Moisseiev, Department of Ophthalmology, Tel Aviv Medical Center, Weitzman 6 St., Tel Aviv, 64239 Israel; [email protected] CAN J OPHTHALMOL — VOL. 48, NO. 3, JUNE 2013
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Comparison of IOP after PK and DSAEK—Moisseiev et al. Mechanisms that may cause elevated IOP after DSAEK include pupillary block glaucoma, trapping of an air bubble behind the iris and subsequent angle closure, formation of PAS, and response to steroids.11,22 Several comparative studies have established the superiority of DSAEK over PK regarding visual rehabilitation.16,23,24 However, very sparse information exists in published literature regarding the comparative rates of IOP elevation between the 2 surgical techniques. During 12 months of postoperative follow-up, 1 study reported rates of induced glaucoma to be 6.3% after PK and 6.7% after DSAEK,16 and another reported rates of IOP over 25 mm Hg to be 16% after PK and 28% after DSAEK.25 Review of literature revealed no study that was directly focused at the comparison of IOP elevation between the 2 techniques. The purpose of this study was to investigate and describe the changes in IOP during the first postoperative year after PK and DSAEK, and reveal any differences between the 2 surgical techniques.
METHODS Patient selection
After approval by the Institutional Review Board of the Tel Aviv Medical Center, the records of all consecutive patients who underwent PK or DSAEK in our institution between January 1, 2006, and December 31, 2010, were retrospectively reviewed. All included patients were 18 years or older at the time of surgery, and their indication for surgery was either pseudophakic bullous keratopathy (PBK) or Fuchs endothelial dystrophy. Only pseudophakic patients with intraocular lens (IOL) within the capsular bag throughout the follow-up period were included. Inclusion in the study also required complete documentation of IOP by Goldmann applanation tonometry (GAT) at all of the following time points: before surgery, upon discharge, and 1 week, 1 month, 3 months, 6 months, and 12 months postoperatively. Patients whose indication for transplantation was due to trauma, herpetic keratitis or keratouveitis, any infectious cause, keratoconus, or a previous failed corneal graft were excluded. Only first procedures were included in this study. Patients who had undergone other techniques of corneal transplantation, or whose surgery was combined with any procedure other than cataract extraction and IOL implantation within the capsular bag were excluded. Phakic, aphakic, and pseudophakic patients with anterior chamber, iris fixated, or sulcus IOLs were excluded, as were patients who had previously undergone any other ocular surgery except cataract extraction. Exclusion criteria also included any history of retinal detachment, retinal vascular occlusion, advanced glaucomatous damage, optic neuropathy, or trauma. Patients who were previously treated with subconjunctival, sub-Tenon, or intravitreal steroid injections for any reason, or patients receiving
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systemic steroidal treatments were excluded. Patients with neovascular glaucoma, synechiae, or any previous glaucoma surgery were also excluded; only patients with no previous glaucoma or previous open-angle glaucoma that was controlled by topical treatment were included. In addition, patients whose records were incomplete were excluded from this study. Data collection
Data were retrieved from the medical notes before the surgery, the surgical reports, the in-patient department charts, and the outpatient clinic charts. The parameters recorded included demographic information, history of diabetes mellitus or hypertension, previous ocular history, the indication for the corneal transplantation, number of transplantation, lens status, occurrence of rejection and any postoperative complications, and the need for any additional medical or surgical interventions throughout the follow-up period. Together with the IOP measurements, the number of pressure-lowering agents in use at all time points was also recorded. Combination preparations (such as Cosopt (timolol and dorzolamide) and Combigan (timolol and brimonidine)) were counted as 2 separate agents. For patients who underwent additional procedures for the treatment of glaucoma, IOP values were censored after these procedures. The number of IOP-lowering agents after the procedure was still recorded and analyzed. Surgical parameters included review of surgical technique as documented to ensure uniformity and any additional procedures combined with the corneal transplantation. Parameters recorded for the donor cornea included donor age, number of days between harvest and transplantation, and endothelial cell count by the Noncon Robo SP-6000 specular microscope (Konan Medical, Inc., Hyogo, Japan) when available. Donor corneas were preserved in EUSOLC dextran corneal storage media containing gentamycin sulfate (143 mg/ml; AL.CHI.MI.A. SRL., Padova, Italy) and kept at 41C between harvest and surgery. Surgical techniques
Surgical technique for PK included creating a partial depth circular incision in the cornea using a trephine, followed by full-thickness excision of the recipient cornea using curved corneal scissors. The donor corneal button was cut by a punch trephine and sutured in place, typically using either 16 interrupted or 8 interrupted and one 16-byte running 10–0 nylon sutures. Surgical technique for DSAEK included stripping of central Descemet’s membrane and endothelium. The donor cornea was cut horizontally with a turbine-driven Moria CB Microkeratome (Moria, Versailles, France) and a 300-mm head. The posterior lamella was then trephined to the size chosen by the surgeon (typically 8.0–9.0 mm in diameter) and inserted into the anterior chamber using one of several techniques, including Busin and Tan glides
Comparison of IOP after PK and DSAEK—Moisseiev et al. Table 1—Baseline information of patients who underwent penetrating keratoplasty versus Descemet’s stripping automated endothelial keratoplasty Parameter
PK (n ¼ 19)
DSAEK (n ¼ 34)
75.8 10 (52.6) 5 (26.3) 14 (73.6) 15.52 6 (31.5) 0.15
74.5 15 (44.2) 7 (20.6) 21 (61.8) 15.53 14 (41.1) 0.25
Mean age, y Male sex, n (%) Diabetes mellitus, n (%) Hypertension, n (%) Mean preoperative IOP, mm Hg Previous glaucoma, n (%) Mean preoperative number of IOP-lowering agents
There was no statistically significant difference between groups in any of the parameters (p 4 0.05). PK, penetrating keratoplasty; DSAEK, Descemet’s stripping automated endothelial keratoplasty; IOP, intraocular pressure.
and suture pull-through. All wounds were sutured using interrupted 10–0 nylon sutures. Air was injected into the anterior chamber under the donor tissue. Either iridotomy or mydriatics were used to prevent pupillary block. Patients were instructed to remain supine for 3 to 6 hours after surgery. After both types of surgery, all patients were treated with topical ofloxacin 0.3% and either dexamethasone sulfate 0.1% or prednisolone acetate 1% four times a day. Dosage was tapered over a year after surgery. Statistical analysis
Correlations between continuous variables were analyzed using Pearson correlation coefficient. t test was used to compare continuous variables between groups. w2 test was used to analyze associations between categorical parameters. Analysis of variance with repeated measures over time was used to analyze the difference in IOP between the 2 surgical techniques. A p value of 0.05 was used to declare statistically significant difference between groups for all analyses. Data were analyzed using SPSS for Windows, version 17.
RESULTS Fifty-three eyes of 53 patients fulfilled the inclusion criteria and were included in the study. Surgeries consisted of 19 (35.8%) PK procedures and 34 (64.2%) DSAEK procedures. The patients in the study included 25 (47.1%) men and 28 (52.9%) women, with a mean age of 75.0 ⫾ 8.8 years (range 52–92 years). There was no statistically significant difference in any of the demographic parameters between both patient groups (Table 1).
Indications for surgery included 42 (79.2%) cases of PBK and 11 (20.8%) cases of Fuchs endothelial dystrophy. The distribution of the indications for surgery varied between the groups, as 9 (81.8%) of 11 cases who had surgery because of Fuchs endothelial dystrophy underwent DSAEK (Table 2). Mean corneal donor age was 59.8 ⫾ 15.0 years (range 12–80 years). Mean time between harvest and transplantation was 4.0 ⫾ 1.9 days (range 1–7 days). Endothelial cell count was available for 23 (43.4%) of the donor corneas and had a mean of 2736 ⫾ 274 cells/mm2 (range 2056–3205 cells/mm2). Donor age was significantly younger, and endothelial cell counts were significantly higher in DSAEK surgeries compared with PK. Time between harvest and surgery was similar in both groups (Table 3). IOP analysis
There was no significant difference in preoperative IOP values (Table 1) or the number of IOP-lowering agents used by patients who underwent PK or DSAEK. Analysis of variance with repeated measures over time was used to compare the IOP during the first 12 months after surgery between the 2 surgical techniques. Patients who had undergone DSAEK had statistically significant lower IOP throughout this period in comparison with those who had undergone PK (p ¼ 0.028; Fig. 1). The number of IOP-lowering agents was not statistically different at any time point between these 2 patient groups (Fig. 2, Table 4). Thirty-three (62.2%) patients were treated with at least 1 IOP-lowering agent at any point throughout the followup. At 12 months, 13 (68.4%) PK patients were treated with at least 1 IOP-lowering agent, compared with 18 (52.9%) DSAEK patients (p ¼ 0.27; Table 4). There was no significant difference in the number of hypotensive agents or the number of subjects who required IOPlowering medication between the groups. Surgical intervention to control elevated IOP was required in 5 (9.4%) patients (2 [11%] PK and 3 [9%] DSAEK; p ¼ 0.82) and was decided upon by glaucoma subspecialists who also monitored these patients. One patient (1.8%) who underwent PK required surgical synechiolysis because of formation of PAS, and another patient (1.8%) underwent Ahmed valve implantation. Two patients (3.7%) who had undergone DSAEK underwent trabeculectomy, and 1 patient (1.8%) underwent Ahmed valve implantation. IOP returned to the normal range in all 5 cases. Measurements of IOP values over 21 mm Hg or at any time point throughout the follow-up were recorded in 13
Table 2—Distribution of indications for surgery Indication for Surgery Pseudophakic bullous keratopathy, n (%) Fuchs endothelial dystrophy, n (%)
Total (N ¼ 53)
PK (n ¼ 19)
DSAEK (n ¼ 34)
p
42 (79.2) 11 (20.8)
17 (89.4) 2 (10.6)
25 (73.5) 9 (26.5)
0.14 0.18
PK, penetrating keratoplasty; DSAEK, Descemet’s stripping automated endothelial keratoplasty
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Comparison of IOP after PK and DSAEK—Moisseiev et al. Table 3—Donor cornea information and comparison between penetrating keratoplasty and Descemet’s stripping automated endothelial keratoplasty Donor Cornea Parameter Mean donor age, y Time between harvest and surgery, days Mean endothelial count, cells/mm2
Total
PK
DSAEK
p
59.8 4.0 2736 (N ¼ 23)
65.8 4.2 2587 (n ¼ 10)
56.5 3.9 2850 (n ¼ 13)
0.029 40.05 0.018
PK, penetrating keratoplasty; DSAEK, Descemet’s stripping automated endothelial keratoplasty
(68.4%) patients who had undergone PK and 9 (26.5%) patients who had undergone DSAEK. This difference was statistically significant (p ¼ 0.015). Measurements of IOP values over 30 mm Hg at any time point throughout the follow-up were recorded in 6 (31.5%) patients who had undergone PK and 5 (14.7%) patients who had undergone DSAEK. This difference was also statistically significant (p ¼ 0.022; Fig. 3). Neither indication for surgery was correlated with IOP. Patient age, sex, and the presence of diabetes mellitus or hypertension did not correlate with IOP. Glaucoma before surgery did not correlate with IOP and was not associated with an increased rate of IOP measurements greater than 21 or 30 mm Hg throughout the follow-up period. These findings were also maintained in a separate analysis for each surgical technique. Combination of corneal transplantation with cataract extraction also did not correlate with IOP.
Complications
Rejection occurred within 12 months of surgery in 1 (1.9%) case in our series. The patient underwent PK and was treated for rejection with intensive topical steroidal treatment 3 months after the procedure.
Fig. 1 — Comparison of mean intraocular pressure values between patients who underwent penetrating keratoplasty (PKP) and Descemet’s stripping automated endothelial keratoplasty (DSAEK) at the measured time points throughout 12 months after surgery. The differences were statistically significant at all postoperative time points.
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Complications encountered during the follow-up period included 2 (3.8%) persistent large corneal erosions and 2 (3.8%) corneal ulcers. Both cases with persistent corneal erosions occurred in patients who underwent PK. One patient in each group was complicated by a corneal ulcer. Although the occurrence of rejection and other postoperative complications was higher in patients who had undergone PK, they did not correlate with IOP.
DISCUSSION This is the first study, to our knowledge, to directly compare IOP elevation between 2 common techniques of corneal transplantation, DSAEK and PK. We found that DSAEK is associated with significantly lower postoperative IOP than PK (Fig. 1), despite similar use of IOPlowering agents during the study period (Fig. 2). This finding has been significantly demonstrated in our study over 12 months of follow-up after surgery in pseudophakic patients who underwent corneal transplantation because of endothelial dysfunction. Complication rates were similar in both groups of patients. Endothelial dysfunction caused by Fuchs endothelial dystrophy or PBK currently constitutes the most common indication for corneal transplantation.11 Both indications are suitable for treatment by PK or DSAEK, but DSAEK is usually favored in Fuchs endothelial dystrophy.16,24,25
Fig. 2 — Comparison of mean number of intraocular pressure–lowering agents used by patients who underwent penetrating keratoplasty (PKP) and Descemet’s stripping automated endothelial keratoplasty (DSAEK), at the measured time points throughout 12 months after surgery. No statistically significant differences were found between the 2 groups.
Comparison of IOP after PK and DSAEK—Moisseiev et al. Table 4—Number and percentage of penetrating keratoplasty and Descemet’s stripping automated endothelial keratoplasty patients who were treated with at least intraocular pressure–lowering agent at all time points Group PK (N ¼ 19) DSAEK (N ¼ 34)
Before Surgery 6 (31.5%) 14 (41.1%)
1 wk
1 mo
3 mo
6 mo
12 mo
9 (47.3%) 11 (32.3%)
10 (52.6%) 15 (44.1%)
13 (68.4%) 17 (50%)
11 (57.9%) 18 (52.9%)
13 (68.4%) 18 (52.9%)
There was no significant difference between the groups at any time point. PK, penetrating keratoplasty; DSAEK, Descemet’s stripping automated endothelial keratoplasty.
Our results reflect this clinical preference, as most patients with Fuchs endothelial dystrophy underwent DSAEK (Table 2). However, only these 2 indications were included in this study, and they were grouped together because they share a common underlying pathologic mechanism of endothelial dysfunction, are treatable by both PK and DSAEK, and have similar outcomes by both surgical procedures.16,23–25 The purpose of this study was to compare IOP between PK and DSAEK. Patients were grouped accordingly. To reduce confounding factors that may interfere with proper comparison, we used strict inclusion and exclusion criteria, and the 2 groups are basically homogenous regarding patient age, sex, indication for surgery, lens status and ocular anatomy, previous background, ocular history, and baseline IOP (Table 2). The only significant differences between the 2 groups concern the donor cornea, which came from younger donors and had higher endothelial counts in patients who underwent DSAEK (Table 3). These differences represent a selection bias of donor corneas for DSAEK procedures but may be compensated by the higher early postoperative rate of endothelial cell loss compared with PK.25–28 Measurements of IOP greater than 21 mm Hg and greater than 30 mm Hg throughout this time were significantly more common in patients who underwent PK (Fig. 3). This finding is in accordance with a previous study that reported a higher incidence of IOP greater than
Fig. 3 — The occurrence of intraocular pressure elevation greater than 21 mm Hg and greater than 30 mm Hg throughout the follow-up period in patients who underwent penetrating keratoplasty (PKP) and Descemet’s stripping automated endothelial keratoplasty (DSAEK). The differences were statistically significant.
25 mm Hg after PK compared with DSAEK.25 Need of medical and surgical interventions to control IOP was not significantly different between the groups. No study had previously focused on this issue, and published literature offers no explanation to this difference. We propose several possible reasons for the tendency of IOP to be higher after PK. First, PK mandates disruption of the structural integrity of the eye, and it is likely that angle distortion and collapse of the trabecular meshwork are more significant during this procedure than in DSAEK. Second, it is possible that postoperative intraocular inflammation and formation of PAS are more frequent and severe after PK. This may also be related to the disruption of ocular integrity during surgery. Third, numerous tight corneal sutures are required in PK, and they may cause additional angle distortion in comparison with DSAEK, which is virtually sutureless. Finally, it is possible to speculate that the difference in IOP is related to differences in steroidal or IOP-lowering treatments. However, no significant differences between the 2 groups in respect to these 2 factors were noted in this study, and we believe that they did not attribute to the difference demonstrated in our study. The accuracy of GAT is known to be influenced by central corneal thickness (CCT),29,30 and it is possible to assume that the difference in IOP is due to changes in CCT. However, several studies have demonstrated that measurement of IOP by GAT was not influenced by CCT in post-PK eyes2,8,31–33 or in post-DSAEK eyes.33–36 It has also been demonstrated that DSAEK grafts are thicker than PK grafts for up to 12 months after surgery.24,37 Therefore, although CCT was not measured in our study, we conclude it is not the cause of the difference in IOP between the 2 groups. We acknowledge that post-PK and post-DSAEK grafts have different biomechanical properties that may influence IOP measurement by GAT, but measuring these characteristics in vivo is difficult in a clinical setting and is beyond the scope of our study. Previous glaucoma has been correlated with an increased risk for postoperative glaucoma both after PK and DSAEK.1,3,5,21,38,39 Our results did not demonstrate this correlation, and we believe this is due to the exclusion of most types of preexisting glaucoma and the inclusion of only a small number of patients with nonadvanced openangle glaucoma in our study. This is supported by the fact that in the subset of patients with prior glaucoma, the mean number of IOP-lowering agents used before the CAN J OPHTHALMOL — VOL. 48, NO. 3, JUNE 2013
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Comparison of IOP after PK and DSAEK—Moisseiev et al. corneal transplantation was only 1.2, and there was no significant difference in the number of IOP-lowering agents after the transplantation between them and patients without prior glaucoma. Rates of complications other than elevated IOP in this series are comparable with previously published data. Persistent epithelial defects were unique to PK, as expected.25 Graft survival rates have been shown to be equivalent in both PK and DSAEK.16,23–25 Our study included only 1 rejection of a PK graft. Despite this, we believe the series reflects the similar and excellent rates of success of both techniques in patients with endothelial dysfunction. This study is limited by its retrospective nature and medium sample size. However, we believe that the relatively high homogeneity between the groups and wholesomeness of the recorded data partly compensate for these limitations. Another limitation is that IOP-lowering medications were not administered according to a fixed standardized protocol. In general, maintenance of IOP less than 20 mm Hg was the goal of treatment in all patients. We are not aware of any difference in IOP tolerance between the 2 groups. CCT was not measured, and IOP was measured only by GAT and not by any other method that may be more accurate in postkeratoplasty eyes. We note that CCT was not found to influence IOP measurement by GAT in these eyes.2,8,31–36 Another limitation is that IOP measurement by GAT in eyes that underwent PK may be inaccurate regardless of CCT, because irregular astigmatism may result in uneven mires and complicate the GAT measurement and its interpretation. In conclusion, DSAEK is associated with a lower postoperative IOP than PK. This finding is demonstrated significantly by our study over 12 months after surgery in pseudophakic patients who underwent corneal transplantation because of endothelial dysfunction. DSAEK is already the preferred procedure by both corneal surgeons and patients for the treatment of this indication because of its superior visual rehabilitation and better tolerability.11,16–18,23,24 Our results indicate a new advantage of DSAEK over PK and serve to strengthen its preference by practicing ophthalmologists. The lower postoperative IOP after DSAEK may be beneficial in preventing late irreversible visual loss caused by glaucoma in these eyes, in which vision may already be compromised and IOP measurement may be difficult and inaccurate. Further research is required to corroborate our findings in prospective and large-scale studies.
Disclosure: The authors have no proprietary or commercial interest in any materials discussed in this article. REFERENCES 1. Foulks GN. Glaucoma associated with penetrating keratoplasty. Ophthalmology. 1987;94:871-4.
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